如何对比Swift String与NSAttributedString以确保代码可编译？

Great question! Let's break down the key differences between Swift's native String and NSAttributedString, then jump into a working code example that demonstrates how they behave side by side.

Here are the most important distinctions to keep in mind:

• Purpose & Content:
  • String is Swift's built-in type for plain, unstyled text—it only contains character data, no formatting information.
  • NSAttributedString (part of the Foundation framework) wraps a plain string plus a collection of attributes (font, color, underline, paragraph styles, etc.) that define styling for specific ranges of the text.
• Type System Integration:
  • String is deeply integrated with Swift's type system, supporting native features like Unicode correctness, string interpolation, and pattern matching.
  • NSAttributedString is a Cocoa/Cocoa Touch class, so it works seamlessly with UIKit/AppKit components (like UILabel, UITextView), but requires bridging when used with pure Swift code.
• Mutability:
  • For String, you use var for mutable instances and let for immutable ones.
  • For attributed strings, there's a dedicated NSMutableAttributedString subclass for modifying content or attributes after creation.

This code runs in an iOS playground or a standard iOS project, and visually shows the difference between plain and attributed text:

import UIKit
import PlaygroundSupport

// 1. Create a plain Swift String (no styling)
let plainText: String = "Hello, Swift & Attributed Strings!"

// 2. Build an NSAttributedString with multiple styles
let styledAttributedText: NSAttributedString = {
    let baseString = "Hello, Swift & Attributed Strings!"
    let mutableAttributedString = NSMutableAttributedString(string: baseString)
    
    // Define styling attributes
    let boldFont = UIFont.boldSystemFont(ofSize: 18)
    let redTextColor = UIColor.systemRed
    let underlineStyle = NSUnderlineStyle.single.rawValue
    
    // Apply attributes to specific text ranges
    // Bold the "Hello," substring
    mutableAttributedString.addAttribute(
        .font, 
        value: boldFont, 
        range: NSRange(location: 0, length: 6)
    )
    // Color "Swift" red
    mutableAttributedString.addAttribute(
        .foregroundColor, 
        value: redTextColor, 
        range: NSRange(location: 7, length: 5)
    )
    // Underline "Attributed Strings"
    mutableAttributedString.addAttribute(
        .underlineStyle, 
        value: underlineStyle, 
        range: NSRange(location: 13, length: 18)
    )
    
    return mutableAttributedString
}()

// 3. Create a simple UI to display both text types
let containerView = UIView(frame: CGRect(x: 0, y: 0, width: 320, height: 220))
containerView.backgroundColor = .systemBackground

// Label for plain text
let plainLabel = UILabel(frame: CGRect(x: 20, y: 40, width: 280, height: 40))
plainLabel.text = plainText
plainLabel.font = UIFont.systemFont(ofSize: 16)
containerView.addSubview(plainLabel)

// Label for attributed text
let attributedLabel = UILabel(frame: CGRect(x: 20, y: 100, width: 280, height: 80))
attributedLabel.attributedText = styledAttributedText
attributedLabel.numberOfLines = 0 // Allow line wrapping
containerView.addSubview(attributedLabel)

// Show the UI in the playground
PlaygroundPage.current.liveView = containerView

What this code does: #

• The plainText variable is a standard Swift String—when displayed, it uses the label's default font and color with no special styling.
• The styledAttributedText uses NSMutableAttributedString to apply three different styles to specific parts of the same base string.
• We add both text types to UILabels so you can directly compare the plain vs. styled output.

内容的提问来源于stack exchange，提问作者Eric Armstrong